1. Field of the Invention
The present invention relates generally to improved systems for mounting batteries on spacecraft to assure their integrity, operability, and long life. Throughout this disclosure, the term "spacecraft" will be used in the generic sense to refer to spacecraft of all types whether they be launch vehicles, space stations, satellites, space probes, or other vehicles operable in a space environment.
2. Description of the Prior Art
Nickel hydrogen batteries for spacecraft are typically mounted into the structure of the spacecraft by means of a plurality of cylindrical metallic sleeves which supportively receive individual cells. The functions of the sleeves are to (a) physically connect each cell to the battery structure and (b) conduct waste heat due to the operation of the cell to the base plate of the battery and thence to the spacecraft heat rejection system (e.g., an optical space radiator).
Numerous metals have been proposed for the fabrication of the battery cell sleeves. These have included aluminum, beryllium, magnesium and alloys of these metals. In actual fact, aluminum is the metal most commonly employed for this purpose. All of these materials meet the technical requirements of having high thermal conductivity, adequate ultimate strength, generally good fracture resistance, and low density. As is common in all space-related activities, weight is a serious consideration in the design and construction of battery cell sleeves such that materials other than metals are continuously being sought which possess all the characteristics noted above while being significantly lighter in weight.
In recent years, composite materials have more and more become materials of choice to replace metals in applications requiring strength and light weight. Composite materials, or "composites", incorporate clusters of elongated fibers of strong materials embedded in a slurry-like amorphous matrix which subsequently solidifies and binds the fibers together into a strong unit.
Graphite is a material which has outstanding thermal conductivity, especially in the pyrrolic form, and low density (.about.2g/cm2). Pure graphite, however, is extremely brittle and for this reason, its use as a sleeve material has not previously been seriously considered. An additional non-technical but significant economic impediment to the use of graphite is that it can only be fabricated into formed parts from solid monoblocks by expensive machining.
A number of examples will now be presented which are representative of the prior art generally relating to this area of technology.
U.S. Pat. No. 5,310,141 issued May 10, 1994 to Homer et al. discloses cylindrical battery cells coupled together in plural sets by pairs of half-shell sleeves. The sleeves conduct heat preferentially in an axial direction. Each sleeve set is mounted onto a heat rejection plate for direct radiation to space.
U.S. Pat. No. 5,096,788 issued Mar. 17, 1992 to Bresin et al. discloses a battery pack having a housing and a plurality of cells within the housing, each cell having a positive and negative terminal, and a flex circuit interconnecting the plurality of cells with a biasing appliance providing appropriate contact between the flex circuit and the cell terminals.
U.S. Pat. No. 4,828,022 issued May 9, 1989 to Koehler et al. discloses a heat conducting sleeve designed to fit around a cylindrical heat source such as a battery for use in a satellite. The design is chosen to obtain the optimum tradeoff between heat transfer capability of the sleeve and its weight for a given application.
U.S. Pat. No. 4,420,545 issued Dec. 13, 1983 to Meyer et al. discloses a pressurized metal-gas battery with emphasis upon reducing weight and volume. End plates axially compress the electrode stack and support it radially within the pressure vessel. This reduces stack stress during vibration and cell cycling. The stack is not bonded to the pressure vessel at any point in the battery but is a free unit confined only by the vessel boundary.
U.S. Pat. No. 4,346,151 issued Aug. 24, 1982 to Uba et al. discloses a multicell sealed rechargeable battery including an open mouth monoblocks container formed of a plurality of cup-shaped cell holders interconnected at mutual tangent zones, electrochemical cells of the rechargeable type fitting into the cell holders and interconnected to form the battery, and a closure member attached to the mouth of the monobloc container.
The concept of using thermally conductive graphite fibers as a light weight material for a nickel hydrogen cell sleeve is the subject of U.S. Pat. No. 5,510,208 issued Apr. 23, 1996 to Hall et al. In this prior invention, a cylinder of axially oriented graphite epoxy fiber is reinforced on the inner and outer surfaces with square weave structural graphite epoxy laminate and replaces a conventional aluminum part. To provide interface compatibility with the aluminum part, the graphite epoxy part has adhesively attached to it features to clamp the cylinder to the cell and to structurally integrate the cell sleeve assembly so formed with other cell sleeve assemblies. The cylinder is partially split in the axial direction to form a key way which provides movement for radial compression.
It was in light of the state of the technology as just discussed that the present invention was conceived and has now been reduced to practice.